Condensed tannins. Structure of the "phenolic scids"

Abstract

Conifer bark-derived condensed tannins can be used in formulating adhesives. Under some extraction conditions and during normal adhesive formulation, the tannin is exposed to strongly alkaline conditions. Alkaline rearrangement results in partial or total rearrangement of tannins of the procyanidin class to "phenolic acids" which have less phloroglucinol functionality. This makes the tannin less suitable for use in adhesives since it is the phloroglucinolic A-ring that gives tannins their characteristic high reactivity with formaldehyde and/or hydroxybenzyl alcohols. The extent of rearrangement depends on the pH and temperature of the solution, more severe conditions give a greater extent of reaction. The structure of the phenolic acids was determined using ¹³C NMR.

Keywords

Polyphenol, procyanidin, bark extract, pine tannin, adhesives, phenolic acids, loblony pine, Pinus taeda L.

Citation

Laks, Peter E.; Hemingway, Richard W. 1987. Condensed tannins. Structure of the "phenolic scids". Holzforschung 41:287-292